The presence of Toxoplasma endozoites in tissue from chronically infected mice was demonstrated by differences in survival of endozoites and cysts in pepsin-HCl. This may be important in explaining reactivated toxoplasmosis in immuno-compromised hosts. An ELISA for the detection of gut-associated circulating anodic proteoglycan (GASCAP) using specifically labeled antibody to GASCAP has been developed. Using this assay, circulating antigen has been found in sera from patients with schistosomiasis. Antigen, however, was not detected in sera from patients two months post-treatment.